1. Field of the Invention
The present invention relates to a process of combusting a particulate or powdery material in a fluidized-bed furnace or incinerator.
2. Prior Art
Fluidized-bed incinerators burn particulate or powdery materials such as dried sludge while being suspended in an upward stream of combustion air introduced through the bottom of the incinerator. A material to be burned is continuously fed into the incinerator in which a fluidized-bed is generated. When finely divided solids are supplied in too small an amount, no sustained combustion is possible, and conversely when the amount of the material supplied is too great, the temperature within the incinerator becomes so high that clinker is formed in the incinerator. To cope with such a problem, it has been customary to continuously detect the temperature in the incinerator and control the supplied amount of the solid material such that the interior of the incinerator will be normally in the range of from 700.degree. C. to 1,000.degree. C. during combustion. It is known that ordinary sludge in order to be burned with an stoichiometric amount of air should be combusted at a stoichiometric temperature of approximately from 1,600.degree. C. to 1,800.degree. C. It follows that to burn the solid material at a temperature ranging from 700.degree. C. to 1,000.degree. C., an amount of air which is about twice as much as a stoichiometric amount of air is needed resulting in a tendency for nitrogen oxides to be formed and discharged during the burning process.